Style is a description about the object - the color, texture and effects it uses. Style doesn't store the info about the shape of the object.

The idea behind the styles is to load only the atributes to already defined shape.

You have 2 ways to do that:

To add a object to the Style list, first you have to have style list visible ( View - Styles) then select the object which style you want to save then click on the Style list with the RIGHT mouse button and select Add to Styles.
The style will be added at the end of the list.
Note: The styles are separate *.sty files in the directory Styles. Do not delete any style manualy by deleting the file, (unless you remove all styles) instead remove the style by clicking on the Style list with Right mouse button and select Remove Style.